Bank cards, credit cards and other forms of electronic data cards have become more sophisticated over the years. In particular, it is now becoming more common to find display technology incorporated into such cards as well as other forms of smart cards, smart labels, and a variety of other devices. In this manner, such card devices may include a user-friendly display that may be employed in conjunction with the card. For example, the display may allow the card user to take advantage of security features such as one-time password (OTP) generation.
Unlike a laptop computer, personal digital assistant (PDA), or even a cell phone, electronic data cards, such as a conventional bank card, are generally lower cost items. That is, they may be mass produced and stored in bulk as “blanks”, devoid of any substantial electronic data prior to activation. In the case of a bank card, customer account access information may be loaded onto the card at the time of activation, for example, by the bank teller or the customer. Barring activation, however, the card remains a small, otherwise disposable, shelved blank of minimal value, with perhaps little care afforded to its manner of storage.
In light of the nature of electronic data cards as noted above, larger, more sophisticated, higher cost, and less durable display technology options may be avoided in providing display capacity thereto. For example, higher cost liquid crystal display (LCD), organic light-emitting diode (OLED), electroluminescence (EL), field emission display (FED), and other display technologies may be avoided. Rather, as noted below, the generally more durable, lower cost option of electrochromic display technology is often preferred.
An electrochromic display is one in which an electrochemical reaction takes place through an electrochromic composition which includes an electro-active ink material. In this manner, pixels are activated to display a pattern in the form of letters, numbers, or other symbols. The display itself is of a stacked configuration that includes a transparent conductive frontplane positioned over a backplane. The backplane serves as a substrate to accommodate circuitry for creating the image of the display, whereas the electrochromic composition is provided thereon, sandwiched between the backplane and the transparent conductive frontplane. An adhesive seal is also positioned between the backplane and the frontplane at a perimeter about the electrochromic composition so as to help keep the composition in place.
The above noted electrochromic composition is made up of a conventional polymer and solvent with electro-active, color-changing components and opacifier disbursed therein. Additionally, a pouring agent, generally silicon dioxide (fumed silica), is added to the composition as an aid in manufacturing of the display card. A variety of other agents may also be incorporated into the composition to help tailor reactivity, rheology, and other characteristics thereof. However, the overall life of the display card is largely determined by how long the composition is able to retain its fluid character. That is, visible perception of induced electrochromaticity through the display diminishes as the fluidity of the composition is reduced. Similarly, the emergence of large particles generated within the composition may inhibit the visibility of an image generated by the display.
As noted above, the composition is held in place between the frontplane and backplane by a conventional adhesive seal. Further, the fluid character of the composition is provided primarily by the solvent. Unfortunately, adhesive seals are susceptible to leakage by a composition's solvent over time. For example, a conventional solvent such as propylene carbonate may initially make up about 40% of the composition. However, depending on a variety of factors, such as adhesive choice and seal design, it would not be uncommon to see such a composition with solvent at 12% or less of the total composition over the course of about 1 to 3 years from manufacture. In such cases, the visualization of the display would no longer be effective.
Additionally, depending on solvent and polymer choice, the utilization of too much pouring agent such as fumed silica tends to induce particle generation over time. For example, in many cases particles of inconsequential size may be present in the composition, but they further have a tendency to ‘flocculate’ with fumed silica and grow in size. These generally harmless particles of inconsequential size may be a result of initial polymer-ink interactions, as is often the case where polyethylene oxide (PEO) and titanium dioxide (titania) are employed. These particles may be of limited size, having no direct effect on visualization of the display image. However, over time these initial particles tend to flocculate with pouring agents such as fumed silica. In certain circumstances this may eventually result in substantial particle generation which may include particles in excess of 100 to 200 microns in size.
With a substantial amount of particle generation of such large particles as noted above, visualization of an image at the display may be impossible. In any case, between the combined problems of substantial particle generation and solvent leakage, a conventional electrochromic display card may have a useful life of substantially less than about 3 years. As a result, electrochromic display cards remain fairly impractical for every day longer term use, such as in the form of a credit card.